194 GEOGNOSY AND GEOLOGY. 
Toe Ssriss. 
The top series embrace the masses known as Alluvium,'and which are 
even now in process of formation. The term includes both normal and 
abnormal masses, the former containing remains of animals and plants that 
still exist, even including man and his works of art. A portion of the 
alluvium belongs to the prehistoric period ; the rest has been formed either 
before our own eyes or those of our ancestors. Alluvium is divided by 
Hausmann as follows : 
A. Masses which have experienced no Great Change of Position 
Under this head belong: 
a. Beds Formed under the Influence of the Sea, such as accumu 
lations of shells with sand and gravel, which gradually unite into a solid 
shell conglomerate, and often lie at a not inconsiderable height above the 
present level of the sea. 
b. Newest Marine Limestone, of Varying Degrees of Compact- 
ness and Solidity. It is generally of a light color, sometimes colored 
brown by oxyde of iron. It contains numerous remains of marine animals, 
very rarely human bones: pl. 41, fig. 36 shows a human skeleton from 
Guadaloupe. 
c. Coral Reefs, which, partly destroyed, are converted into conglomerate, 
and are no longer inhabited. They frequently have an annular shape, and 
form the atolls or coral islands, of which so many occur in the Pacific ocean 
( pl. 49, fig 2). 
ad. Newest Marine Sandstone, produced by the cementation of littoral 
sand by lime or oxyde of iron. Its colors are white, grey, or red ; and the 
formation exists well developed in the straits between Italy and Sicily. It 
frequently includes remains of marine shells. 
B. Formations produced under the Influence of Running or of Standing 
Water. 
a. Traventine, or Newer Calcareous Tufa. It either forms the 
bottom of pristine lakes or ponds, or is deposited in the vicinity of springs 
or waterfalls. This latter is the case in the cascade of Teverone near 
Tivoli (pl. 52, fig. 5). The traventine sometimes overlies peat, and is 
covered by loam; sometimes it lies on older masses, in which case the 
strata may occupy a rather high level. They are generally accompanied by 
oxydes of iron and manganese, and are sometimes bituminous. Fossils are 
very numerous in single portions, and generally of still living forms, as 
Helix, Planorbis, &c., among shells. Stems. of grass, leaves, moss, &c., 
contribute not a little to the porosity of the rock. Bones of mammalia. as 
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